The present invention relates generally to apparatus and methods for making and inspecting pre-assembled articles, and more particularly to apparatus and methods for inspecting such articles.
Articles such as disposable absorbent garments have numerous applications including diapers, training pants, feminine care products, and adult incontinence products. A typical disposable absorbent garment is formed as a composite structure including an absorbent assembly disposed between a liquid permeable bodyside liner and a liquid impermeable outer cover. These components can be combined with other materials and features such as elastic materials and containment structures to form a product which is specifically suited to its intended purposes. A number of such garments include fastening components which are intended to be connected together (e.g., pre-fastened) during manufacture of the garment so that the product is packaged in its fully assembled form.
For example, one such pre-fastened garment is a child's training pants, which have a central absorbent chassis and front and back side panels extending laterally out from the chassis adjacent longitudinally opposite ends thereof. A portion of each of the front and back side panels has a respective fastening component disposed thereon. During manufacture of the training pants, the central absorbent chassis is initially formed generally flat and then folded over so that the front and back side panels face each other. In pants that have fastening components, the respective fastening components of the front and back side panels are then aligned and connected together to define an engagement seam. Upon securing the front and back side panel fastening components together, the pre-fastened pair of training pants is in its fully assembled three-dimensional form having an interior space bounded in part by the engagement seam.
For quality control purposes, it is often desirable to monitor the presence of and/or interrelationships between one or more elements of a disposable absorbent garment. For instance, elements such as outer covers, liners, absorbent pads, side panels, elastic components, fastener components, etc. must be positioned or aligned with respect to each other and/or to other components as desired or otherwise intended in order to produce an acceptable product. Accordingly, inspection systems are commonly used to detect the presence and/or relative positions of such components during manufacturing. If an inspection system determines that one or more components are out of position and thus do not properly register with other components, the inspection system typically outputs one or more signals indicating that certain articles should be culled and discarded, that the process should be adjusted so as to bring out-of-position components into proper position, that the process should be adjusted so that subsequent components are brought into proper registration with one another, etc.
One such registration inspection system is disclosed in U.S. Pat. No. 5,359,525, the disclosure of which is incorporated herein by reference. As described therein, registration inspection of a composite product during fabrication is accomplished by producing an image of the article and then analyzing the image to detect the relative positions of one or more components. The detected positions are then compared to desired positions to thereby determine whether one or more components are improperly positioned. This registration inspection system employs conventional video cameras for capturing visible and ultraviolet light reflected by and/or transmitted through components of the product in order to produce still video images of such components. Thus, after producing a video image of a composite article and its several components, the image can be analyzed to determine whether the components are properly positioned and registered with one another.
Although highly useful for many applications, the inspection system disclosed in the aforementioned patent has certain shortcomings with respect to the inspection of engagement seams formed by connecting two elements together such that the engagement seam is essentially two layers. For example, formation of engagement seams formed by connected side panels of the training pants described previously has heretofore entailed connecting the side panels in face-to-face relationships with outer edges of the side panels aligned with each other. To inspect such an engagement seam, it was necessary only to inspect the exposed outer edges of the side panels so that there was no need to actually capture an image of any underlying elements or edges of the training pants.
However, more recent engagement seams are formed by connecting the side panels in overlapping relationship so that the outer edge of one side panel underlies the other side panel at the engagement seam. One problem associated with inspecting such seams is that the lap seam is not held flat against the light source. This may cause the image to appear fuzzy because the seam is not at the correct focal length for the camera. A second problem is the seam not lying flat against itself. The machine vision system camera captures a two dimensional image of the seam. Therefore, if the seam is not flat, the seam overlap may appear smaller than it actually is.